1. Field of the Invention
The present invention relates to a radio frequency front-end circuit that transmits and receives radio frequency signals.
2. Description of the Related Art
A variety of radio frequency front-end circuits have been designed so far. One example of the radio frequency front-end circuits includes a duplexer that is a combination of a transmission filter and a reception filter, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-120295.
In the duplexer, respective one ends of the transmission filter and the reception filter are connected to each other at a common terminal, and the common terminal is connected to an antenna or an antenna-side circuit. The other end of the transmission filter is connected to a transmission circuit, and the other end of the reception filter is connected to a reception circuit.
In the radio frequency front-end circuit of the above-described type, as a result of having a configuration in which the transmission filter and the reception filter are connected to each other, an impedance is set such that the circuit is opened at a fundamental frequency of a transmission signal when looking at the reception filter side from the transmission filter side, to prevent the transmission signal from coming into the reception filter side.
In the radio frequency front-end circuit of the related art, however, it is found that receiving sensitivity in the reception circuit connected to the reception filter degrades even in the case of trying to secure isolation between the transmission filter and the reception filter as described above.